1. Field of the Invention
The invention relates to a shutoff device for a gas or line, in particular one having a large cross section, with a gas duct or line housing which can be integrated into the gas duct and with at least one shutoff mechanism, in particular a movable shutoff valve, whereby the shutoff mechanism has a plate-shaped shutoff body, which in the shutoff position is in sealed contact against a seal seat permanently connected to the gas line housing, thereby separating the chambers of the gas line located on different sides of the shutoff mechanism from one another, and whereby the seal seat in the peripheral region of the plate-shaped shutoff body extends around its entire circumference.
2. Background Information
Shutoff devices of the type mentioned above are used in practice in many different embodiments. To shut off lines conducting gas and exhaust gas, i.e. pipelines and ducts, for example, the prior art includes the use of blank disk inserts, which employ the principle of a blind flange shutoff.
Since the capacity of current and future systems will continue to increase, the corresponding gas lines must also be designed with increasingly greater dimensions. In the course of these increases in capacity, the responsible safety authorities have also allowed or certified safety devices which contain two shutoff valves located one behind the other in the direction of the gas flow, i.e. two shutoff levels, one some distance behind the other. The space thereby formed between the shutoff valves, however, must be filled with a buffer or barrier medium, the pressure of which buffer medium is higher than the forward pressure--i.e. the pressure of the first shutoff valve--in the gas flow direction. The buffer medium prevents the passage of the potentially dangerous gas, so that maintenance personnel are not exposed to the gas. The buffer medium can be air.
A further consideration with these gas lines to be shut off is that they often transport corrosive gases, e.g. exhaust gases from coal-fired boiler systems, when they are used as part of an exhaust gas desulfurization system. When operating conditions cause the temperature to fall below the acid dew point of these gases, highly-concentrated acids are formed very quickly. These acids precipitate on the cold sides of the valves of a closed shutoff valve and cause corrosion damage there (e.g. so-called "pitting"). Damages of this type can be detected on the double valves described above as a result of a drop in the pressure of the buffer medium, so that appropriate measures can be taken to repair these damages before there is acute danger to the lives of the operating and maintenance personnel. In other words, the damaged valve would allow the dangerous gas to pass, which could put the operating personnel in danger. It can be easily understood, however, that these shutoff devices, with several shutoff valves and/or shutoff levels located in series, not only take up a relatively great amount of space, but are also relatively expensive.